Procedures · Lower Extremity

Ankle Positioning Series

Explore the ankle's anatomy, then use Practice mode to position the AP, mortise, oblique, and lateral projections yourself.

Ankle

Right

StudyBucky

Loading model…

Hover a bone, name it, then click to check · drag to rotate

The routine ankle series

The projections this region is examined with. Set them up yourself in Practice positioning.

AP ankle

Anteroposterior projection · leg unrotated

Demonstrates: The ankle in true frontal profile — distal tibia and fibula, the tibial plafond, both malleoli and the talus, with the proximal half of the metatarsals included. The distal tibiofibular joint stays partly closed and the lateral part of the mortise is not fully open.
Part position: Supine, leg fully extended, ankle centred. The foot is left in its natural position — dorsiflexion is not forced. The whole leg stays unrotated, so the intermalleolar line is not parallel to the image receptor.
Central ray: 90° to the image receptor, centered midway between the malleoli.
Why it is positioned this way: This is the unrotated baseline. Because the lateral malleolus sits further back than the medial, a true frontal projection superimposes part of the distal fibula behind the tibia and talus. That overlap is not a positioning error — it is the reason a separately rotated projection has to exist at all.

Also covered by this projection

AP stress (inversion / eversion)Same projection geometry, with the ankle stressed to test the collateral ligaments. Widening of the mortise joint space indicates ligament laxity or a tear. The beam-to-part relationship is unchanged, so it shares this view.

AP weight-bearingSame projection geometry, taken erect under load, so the joint is seen bearing weight rather than at rest.

Mortise (AP oblique, 15–20° medial rotation)

AP oblique projection · medial rotation 15–20°

Demonstrates: The whole ankle mortise — the three-part joint space between the talus and the socket formed by the tibia and fibula — open across the entire talar surface, with both malleoli in profile. Only minimal superimposition should remain at the distal tibiofibular joint.
Part position: Supine as for the AP, then internally rotate the entire leg and foot together about 15–20°, until the intermalleolar line lies parallel to the image receptor. The foot stays in its natural plantar-flexed position rather than being dorsiflexed, which keeps the base of the fifth metatarsal — a common fracture site — in view.
Central ray: 90° to the image receptor, centered midway between the malleoli.
Why it is positioned this way: The intermalleolar plane already sits about 15–20° to the coronal plane, because the lateral malleolus lies further posteriorly. Rotating by exactly that amount brings the plane parallel to the receptor and turns the fibula clear of the talus, which is what opens the lateral mortise.

45° AP medial oblique

AP oblique projection · medial rotation 45°

Demonstrates: The distal tibiofibular joint, open with no more than minimal overlap in an average patient, along with the sinus tarsi and the base of the fifth metatarsal. The lateral malleolus and talus show little or no superimposition, while the medial malleolus and talus stay partly superimposed.
Part position: Supine as for the AP, then rotate the leg and foot together 45° medially, turning them as a unit. Where the patient can tolerate it, dorsiflex the foot so the plantar surface sits at least 80–85° to the image receptor.
Central ray: 90° to the image receptor, centered midway between the malleoli.
Why it is positioned this way: 45° is where the fibula clears the tibia at the distal tibiofibular joint. Under-rotate and the tibia still overlaps the fibula; over-rotate and the fibula superimposes the tibia, closing the lateral mortise. The dorsiflexion matters just as much: let the foot stay plantar-flexed more than about 10–15° from vertical and the calcaneus is thrown over the lateral malleolus, hiding the area the projection exists to show. Inverting the foot on its own mimics rotation without actually rotating the leg.

Lateral ankle (mediolateral)

Mediolateral projection · beam enters medial, exits lateral

Demonstrates: The ankle in true lateral profile — talus and calcaneus in profile, the tibiotalar joint open with a uniform space, and the distal fibula superimposed over the posterior half of the tibia. The tuberosity of the fifth metatarsal, the navicular and the cuboid are included.
Part position: Lateral recumbent, affected side down, knee flexed about 45°, with the opposite leg placed behind the injured limb to stop over-rotation. The foot is dorsiflexed so the plantar surface sits at 90° to the leg, as far as the patient tolerates — never forced — which helps hold the true lateral.
Central ray: 90° to the image receptor, centered to the medial malleolus.
Why it is positioned this way: The beam enters the medial surface and exits the lateral, which is what makes this a mediolateral projection rather than a lateromedial one. Rotation is judged off the fibula: in a true lateral it sits superimposed over the posterior half of the tibia.

Also covered by this projection

Lateral weight-bearingTaken erect under load and positioned lateromedial — receptor against the medial side, beam entering laterally. Same lateral profile, opposite beam direction.

Alternative lateromedialA documented alternative to the routine mediolateral, for a patient who cannot be placed on the affected side.

Procedures lessonFoot & ankle